The present invention relates to a lens mount barrel for photographing with a flash lamp in which an operational sleeve for focusing cooperates with a stopdown sleeve.
Generally, a stopdown sleeve is mounted coaxially surrounding a lens mount barrel and is click-stopped at positions where its stopdown scale coincides with a suitable index so that the positional relationship is firmly maintained.
A "flashmatic lens" is also known in which an operational sleeve and a stopdown sleeve are coupled to each other in a lens mount barrel with the two sleeves integrally rotatable together so that the stopdown value may be automatically adjusted to a suitable value by rotation of the operational sleeve for photographing with a flash bulb or electronic strobe. In such a flashmatic lens, a photographic magnification or a distance to the object is adjusted to a value within a sequence of numbers such as 1/2 and 1/4 (which is standardized in the Japanese Industrial Standards with respect to sequences of numbers for photographic distance scales) by rotating the operational sleeve for flash photographing. The stopdown value used is automatically determined on the stopdown scale by the relationship of the guide numbers. The stopdown value is not an exact value in the sequence of f-stop numbers generally used such as 2, 2.8, 4, 5.6, 8, . . . and is, for example, read out as a value near 4 but falling between 4 and 5.6. The stopdown values are usually supplied in the form of a data table or the like. To accomplish a flash photographing operation, the photographer must estimate the proper stopdown value from the table which gives both magnification and stopdown values. In some lens constructions, an interlock mechanism has been provided so as to prevent accidental displacement from a position where the magnification or distance scale is aligned with the index. In this case, after the magnification or distance scale has been suitably set, it is required that the scale be locked after carefully adjusting the index.